The DUs are all versatile, i.e. each DU is able to display any of the EIS or ECAM images. (However, the ECAM DU cannot display PFD/ND images).
 In normal operation, the DMC 1 drives the CAPT PFD, the CAPT ND and the upper ECAM DU through their normal input N. The DMC 2 drives the F/O PFD, the F/O ND and the lower ECAM DU also through their normal input N (the DMC 3 is in standby, ready to take over from the DMC 1 or 2 in case of failure).
 In fact, each DU has two inputs to receive the digital signals from the DMC dedicated buses (master DSDL), one normal input N and one alternate input A (This alternate input is used in some reconfiguration cases following transfer control as explained in the paragraph concerning DU failures).
 1EFF : 106-149, 303-399, 1 31-68-00Page 1 1 1 Config-3 Aug 01/05 1 1 1CES 1

 EFIS/ECAM Reconfigurations Between DMCs and Between DUs
 Figure 001

 1EFF : 106-149, 303-399, 1 31-68-00Page 2 1 1 Config-3 Aug 01/05 1 1 1CES 1 In turn, each DU sends to its driving DMC digital signals through a dedicated bus which is called feedback DSDL. Through this feedback link, the DUs acknowledge proper reception of the DSDL master signals, and also inform the DMC of their detected failures, so that the DMC can make the proper action (for instance, automatic transfer of a PFD image on an ND in case of detected failure of the PFD).

 NOTE : The connections between the DMC 3 and the DUs are crosswired for the
____ PFD and ND, in order to cope with a possible wire cut-off of the connection which delivers the PFD information. In this case, when the DMC 3 supplies the PFD and the ND on one side, CAPT or F/O, the DMC 3 signals enter the PFD and the ND via their alternate inputs. The activation of the DU alternate inputs and the deactivation of the normal inputs is made by the grounding of a discrete input on the DU connector. This is achieved by an A/C circuitry which takes into account all the conditions that lead to the change of inputs (normal or alternate).
 NOTE : All of the DMCs and DUs know their position aboard the A/C by A/C
____
 wiring : straps connected or not connected.

 (Ref. Fig. 002, 003)
 3. EIS Switching Operation
_______________________
 A. EIS DMC Switching There are no cross-talk links between the three DMCs, in order to ensure complete segregation of CAPT and F/O displays.
 Inside the DMCs, downstream of the PFD, ND, ECAM channels, there are
 switching relays for the DSDLs.

 In the event of DMC 1 (or DMC 2) failure, the Captain (or First Officer)
 can switch over to DMC 3. This is controlled by means of the EIS DMC
 selector switch (CAPT/3 or F/O/3 position).
 (Ref. Fig. 004)

 In this case, the DMC 3 totally replaces the DMC 1 (or 2) through the
 stage of the output switching relay of the failed DMC.
 As explained in the previous section, the connections between the DMC 3
 PFD and ND channels and the PFDs and NDs are cross-wired.

 Therefore, it is necessary to send the DMC 3 PFD and ND signals to the
 Alternate inputs of the PFDs and NDs, so that the PFD and ND images
 remain at their normal location.

 1EFF : 106-149, 303-399, 1 31-68-00Page 3 1 1 Config-3 Aug 01/05 1 1 1CES 1

 The relay box (CAPT or F/O) does the selection of the alternate inputs of
 the PFDs and NDs.
 (Ref. Fig. 005)

 NOTE : In the event of DMC failure, the DUs driven by this DMC display a

____ diagonal line, which helps the crew to make immediately the right action.
 The DMC 3 acts as a back up (hot spare). When the EIS DMC selector switch is in NORM position, the DMC 3 works like the DMC 1 as regards the selection of all the input sources, so as to be readily available to take over the driving of the CAPT PFD and ND and of the upper ECAM DU, with minimum transfer delay, as soon as the pilots place the ECAM/ND XFR selector switch in CAPT/3 position. In case of selection of the DMC 3, both the master DSDL and the feedback DSDL buses are switched in the DMC 1 (or 2) output switching stage.
 B. Switching of the EIS DUs (PFD-ND)
 (1)
 Manual PFD/ND transfer (Ref. Fig. 006) A manual transfer facility (by means of PFD/ND XFR P/BSW) enables each pilot to cross-change the images which are displayed on his PFD and ND at any time : at each action on this pushbutton switch, there is an inversion between the two images : the one which was displayed on the left DU is displayed on the right DU and vice versa.

 (2)
 Transfer of the PFD image on the ND

 (a)
 In case of detected failure of the DU which normally displays the PFD image, there is an automatic PFD/ND transfer. The PFD image is presented on the DU which normally shows an ND image. This automatic transfer is controlled by means of a discrete signal generated by the DMC upon recognition of the failure (NORMAL PFD INVALID).
　
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